The present invention relates to picture coding and decoding techniques, and particularly to intra coding and decoding techniques.
MPEG-4 AVC as an international standard of moving picture coding employs a system called intra prediction as an intra coding system for completing processing in one screen. The intra prediction is directed for duplicating a decoded sample value neighboring to a block to be processed in a designated prediction direction thereby to create a prediction picture of the block to be processed. MPEG-4 AVC defines nine prediction directions illustrated in FIGS. 1A and 1B, and is configured to transmit a mode number of an intra prediction mode indicating a prediction direction of each block thereby to designate a proper prediction direction.
The number of defined prediction directions is increased, thereby enhancing prediction picture quality. Reference numeral 201 in FIG. 2A indicates 17 exemplary defined prediction directions, and reference numeral 202 in FIG. 2B indicates 34 exemplary defined prediction directions. However, an increase in defined prediction directions leads to an increase in transmission information of intra prediction modes. As the number of defined prediction directions increases, a rate of intra prediction modes in all the occurred codes increases, and thus the need of an efficient transmitting method enhances.
JP2009-246975A describes therein a means for reducing the amount of codes of intra prediction modes by reducing the total number of intra prediction modes to be transmitted. The method in JP2009-246975A is directed for scanning intra prediction modes of a plurality of blocks for predetermined units of unification and transmitting one intra prediction mode in units of unification when all the intra prediction modes in the units of unification are the same, thereby reducing intra prediction modes to be transmitted.